Production of thermoplastic filamentary yarn

ABSTRACT

A PROCESS FOR PRODUCING YARN HAVING UNDRAWN OR PARTIALLY DRAWN PORTIONS THEREALONG COMPRISING FEEDING THE YARN TO A NIP FORMED BETWEEN TWO ROLLS ONE OF WHICH HAS CIRCUMFERENTIAL GROOVES OF LESSER WIDTH THAN THE YARN WHEREBY LESS THAN ALL OF THE YARN FILAMENTS ARE GIPPED AT ONE TIME, RECIPROCATING THE YARN TRANSVERSELY OF ITSELF WITHIN THE NIP AND WITHDRAWING THE YARN AT SUFFICIENT SPEED TO DRAW EACH FILAMENTAS IT BECOMES GRIPPED BY THE NIP.

United States Patent 3,737,503 PRODUCTION OF THERMOPLASTIC FILAMENTARY YARN Frank Wilding, Harrogate, England, assignor to Imperial Chemical Industries Limited, London, England No Drawing. Continuation-in-part of abandoned application Ser. No. 750,019, Aug. 5, 1968. This application Dec. 3, 1970, Ser. No. 94,939

Int. Cl. D01d 5/20 US. Cl. 264-167 7 Claims ABSTRACT OF THE DISCLOSURE A process for producing yarn having undrawn or partially drawn portions therealong comprising feeding the yarn to a nip formed between two rolls one of which has circumferential grooves of lesser width than the yarn whereby less than all of the yarn filaments are gripped at one time, reciprocating the yarn transversely of itself within the nip and withdrawing the yarn at sufficient speed to draw each filament as it becomes gripped by the nip.

This is a continuation-in-part of application Ser. No. 750,019, filed Aug. 5, 1968, now abandoned.

This invention relates to a process for the productio of synthetic thermoplastic filamentary yarn wherein undrawn or partially drawn filamentary segments occur randomly in and along the yarn.

It is known to produce filamentary yarns composed of synthetic thermoplastic linear polymers which are longitudinally variable in some property, as for example shrinkage when heated. Such yarns have been produced by periodical variation of the heat or the draw ratio applied at the drawing stage or by drawing the yarn at below the natural draw ratio with control of the temperature and humidity of the ambient air in the drawing zone. Such processes all result in filamentary yarns which are longitudinally variable in some property but in which the properties of the individual filaments across the width of the yarn are substantially uniform, at any point. Such known yarns thus have poor physical properties such as tenacity due to the presence of weaker sections in the yarn.

It is an object of this invention to provide a process for producing yarns having variable properties such as dye affinity while substantially retaining their good physical properties.

According to the present invention we provide a process for the production of synthetic filamentary yarn selected from the group consisting of a polyester or a polyamide comprising: feeding the yarn to a nip zone having a plurality of discontinuities disposed transversely of the yarn each of said discontinuities being of insuflicient size to contain all the filaments of a yarn; spreading the yarn across a portion of the nip zone; intermittently gripping and releasing distinct transverse filamentary portions of the yarn in the nip zone in such a manner that at no time is the entire transverse cross section of the yarn gripped simultaneously, said intermittent gripping being effected by reciprocating the yarn transversely of itself across the discontinuities in said nip zone; and passing the yarn to a withdrawal roll operating at a peripheral speed which draws the gripped filaments thereby producing a yarn having random property variations longitudinally along each filament and transversely across groups of filaments at any given position.

Filamentar'y yarn is produced from synthetic thermoplastic linear polymers by the processes of dryor meltspinning in which a solution of the polymer in a solvent volatile at the spinning temperature or the molten polymer is extruded through a spinneret which is a plate having a number of small orifices therein. The extruded filaments, while still plastic due to their heat content or the presence of solvent, are elongated by the tension induced therein by the collection or forwarding means to which they are passed from the spinneret. However, such elongation produces little orientation and to have useful physical properties it is usual to draw or elongate the extruded filaments additionally to the elongation produced in the plastic as-extruded material. Such drawing is carried out at a lower temperature either in the extrusion apparatus or in separate drawing apparatus and produces a marked increase in orientation together with an increased tenacity and a reduced extensibility. The drawing may be efiected by simply applying sufiicient tension to the yarn or a heated or unheated snubbing surface may be used to contact the yarn in the drawing zone between the feed and withdrawal rolls of a drawing apparatus enhancing the ease and rate of drawing possible. In the former case the drawing process is usually irregular and will produce alternate drawn and undrawn segments in the filaments, this irregularity being superimposed upon the random etfect produced in the invention. It is preferred that some snubbing and/ or heating means between the feed and withdrawal rolls is used. Such snubbing means may be, for example, a single ceramic peg which imposes a frictional drag on the yarn passing therearound and may thereby cause the generation of heat or it may be a heated metal snubbing pin which imposes both frictional and heating effects. An additional heating means may be used following the snubbing means to heat treat the drawn yarn before passage over the withdrawal roller. Alternatively the snubbing means or the snubbing means and following heating means may be replaced by a single heating means such as a hot air or vapour bath or a hot liquid bath which imposes primarily a heating eflect to facilitate the drawing process.

The process of the present invention, wherein drawing is carried out non-uniformly and the non-uniformity is applied in a random fashion, may be carried out by a simple modification of the usual drawing equipment. In normal uniform drawing it is necessary to provide a means for preventing slippage of the yarn in its passage over or around the feed roll and this is effected by taking a number of turns of yarn around the roll or by holding the yarn in close contact with the roll by means of another roll, having a resilient surface, pressed thereagainst. The latter roll is commonly referred to as a cott or nip roll.

A modification of the normal drawing equipment by means of which a process according to the invention may be carried out is to provide a series of circumferential grooves in the peripheral surface of the cott roll and to arrange to reciprocate the yarn axially of the feed and cott rolls over a small stroke. The grooves may be continuous for the full circumference or may be a number of arcuate grooves interposed by ungrooved portions of the cott roll surface. Other profiled roll surfaces may also be used provided that there is an adequate discontinuity of contact between the cott roll and the surface of the adjacent feed roll. By these means the filaments comprising the yarn tend to be spread across the feed roll surface and are intermittently and randomly gripped by portions of the cott roll surface between grooves and released by the succeeding grooves which are of insufficient size to contain all the filaments in a yarn at any one time. Thus each filament is alternately subjected to drawing tension and released therefrom effectively in a random fashion. At no time are all the filaments across any section of yarn simultaneously held or released and thus a yarn is produced having random longitudinal and transverse property variations along its length.

Variations in any property, as for example shrinkage or I dye-uptake rate,- which is affected by orientation are thus produced in purely random fashion in the filaments comprising the drawn yarn product. However, due to the random occurrence of these variations and the short intervals over which they occur the grosser properties of the yarn suchas tenacity and extensibility are not significantly altered from those of a corresponding uniformly drawn yarn=.but more sensitive properties, such as'dye-uptake rate are significantly affected and fabrics having an unusual andinteresting speckled or randomv pattern when dyed may be produced from the yarns.

Some thermoplastic linear polymers, as for example poly(ethylene terephthalate) may be of low crystallinity in the undrawn or partially drawn state and filamentary segments of such undrawn or partially drawn polymers may embrittle to some extent by crystallisation when the yarn is heat treated. Deterioration of drawn yarn properties due to this effect is reduced by means of this invention and may be further minimised or reduced by adjustment of any heat treatment of the drawn yarn or alternatively, by increasing the degree of orientation imparted to. the freshly extruded filaments in the plastic state. The degree of such orientation is readily measured and controlled by means of the birefringence of the filaments.

By altering the dimensions of the grooves in the cott roll or by varying the drawing speed or other drawing conditions, as for example the tension in the yarn passing to the feed/cott roll nip, it is possible to vary the effect achieved from one which is quite subtle to one which is very pronounced and at the same time maintain substantially unaltered the physical properties of the yarn and textile vmaterials produced therefrom as for example woven or knitted fabrics or non-woven webs. One usefuland simple means of controlling the random effect of this invention is by varyig the temperature of the snubbing or heating means used to facilitate the drawing process. This method is particularly useful for controlling the effect when drawing polyester filamentary yarns according to this invention. It is found that for poly(ethylene terephthalate) yarns the effect of random drawing decreases with increasing temperature of the yarn at drawing and that all detectable effect of random drawing may be eliminated if the drawing temperature is raised sufficiently;

Yarns according to this invention are very useful in the production of non-woven materials in that ifa pronounced variation is produced in the yarn it will be selfbonding when hot pressed as a non-woven web, bonding taking place mainly at points of contact with the undrawn or partially drawn segments.

The following examples illustrate the invention and the manner in which it may 'be performed.

EXAMPLE 1 'Nylon 66 yarn of 68 filaments and total denier 3850 in the as-extruded state is drawn between feed and draw rolls at a draw ratio of 3.6:1 and a draw roll peripheral speed of 910 ft. per minute (277 metres per minute) with a inch diameter (19 mm.) matt chrome snubbing pinin the draw zone between the rolls. The polytetrafluoroethylene surface of the cott roll in contact with the yarn on the feed roll has circumferential grooves cut in its surface at per inch, each measuring 0.030 inch (0.76 mm.) deep and 0.060 inch (1.5 mm.) wide at the surface the ungrooved portion or land between grooves being 0.040 inch (1.0 mm.) wide. A yarn guide positioned close to the nip between the feed and cott rolls traverses the yarn with a stroke of 1.5 inches (3.8 cm.) at lcycle per. 5

EXAMPLE 2 Nylon 66 yarn as used in the foregoing example is drawn as in that example but with apparatus wherein the grooves are narrower (0.050 inch; 1.27 mm.) and shallower (0.025 inch; 0.64 mm.) and the lands between are wider (0.050 inch; 1.27 mm.). Drawn yarn of 1212 mean denier is produced showing a lower variation of 35% about this value.

- EXAMPLE 3 'Poly (ethylene terephthalate) yarn of 30 filaments and 548 total denier in the substantially undrawn state (birefringence 4.66 10- is drawn between feed and draw rolls at a draw ratio of 3.65:1 over a 2.35 inch (6.0 cm.) diameter matt chrome snubbing pin of surface temperature C. and a 8 inch' (20 cm.) hot plate of surface temperature 185 C. situated between the feed and draw rolls at a drawing speed of 1900 ft. per minute (580 metres per minute). The cott roll is nylon covered and has circumferential grooves of V-cross-section cut in its surface measuring 0.79 mm. wide with lands between of 0.79 mm. width. A yarn guide positioned close to the nip between the feed and cott rolls traverses the yarn with a stroke of 1 inch (2.5 cm.) at 5.5 cycles per minute. Due

.to the impeding effect of the grooved cott roll the yarn in the nip between the feed and cott rolls traverses only over about 0.25 inch (0.64 cm.). The yarn passing to the feed roll is pretensioned to a value of '3 grams.

Drawn yarn of denier is produced which has a tenacity of 4.1 g. per denier and an extension at break of 23%. By comparison a yarn produced from the same starting material using a smooth surfaced cott roll in place of the grooved roll has a tenacity of 4.7 g. per denier and an extension at break of 25% A fabric knitted from yarn drawn using the grooved cott roll when dyed showed a pronounced random pattern of deeper dyed segments which were the undrawn or partially drawn segments.

EXAMPLE 4 Poly(ethylene terephthalate) yarn of 60 filaments and 405 total denier in the substantially undrawn -state (birefringence 16.0 10-. is drawn between feed and draw rolls at a draw ratio of 2.50:1 over a 2.35 inch (6.0 cm.) diameter matt chrome snubbing pin of surface temperature 63 C. and a hot plate as in Example 3 situated between the feed and draw rolls at a drawing speed of 1470 ft. per minute (450 metres per minute). The cott roll is similar in nature and construction to that used in Example 3 and the yarn is traversed by a yarn guide in a similar manner and at a similar frequency as given in that example. The yarn passing to the feed roll is tensioned to a value of 2 grams.

Drawn yarn of denier 161 is produced which has the following properties.

Tenacity; 4.7 g. per denier Shrinkage: 5.2% in boiling water Extensibility: 26.7%

Poly(ethy1ene terephthalate) yarn as used in Example 4 is drawn as in that example but with a pin temperature of 52 C. Drawn yarn of 161 denier is produced which has a tenacity of 4.3 g. per denier, an extensibility of 23.9% and a boiling water shrinkage of 5.5%.

A fabric knitted from this yarn showed a somewhat more pronounced random pattern of deeper dyed segments compared with the fabric of Example 4.

. In all the foregoing examples examination of individual dyed yarns with a magnifying glass confirmed thatthe dye uptake was quite randomly variable in short filamentary segments both transversely and longitudinally in the yarns.

What I claim is:

1. A process for the production of synthetic filamentary yarn selected from the group consisting of polyester or a polyamide comprising: feeding the yarn to a nip zone having a plurality of discontinuities disposed transversely of the yarn each of said discontinuities being of insufficient size to contain all the filaments of a yarn; spreading the yarn across a portion of the nip zone; intermittently gripping and releasing distinct transverse filamentary portions of the yarn in the nip zone in such a manner that at no time is the entire transverse cross section of the yarn gripped simultaneously, said intermittent gripping being effected by reciprocating the yarn transversely of itself across the discontinuities in said nip zone; and passing the yarn to a withdrawal roll operating at a peripheral speed which draws the gripped filaments thereby producing a yarn having random property variations longitudinally along each filament and transversely across groups of filaments at any given position.

2. A process as in claim 1 wherein said nip zone is the zone of contact between a feed roll and a nip roll the surface of one of these rolls having the said discontinuities disposed in an axial direction.

3. A process as in claim 2 wherein the discontinuities are circumferential grooves each of a length equal to the roll circumference.

4. A process as in claim 2 wherein the discontinuities are a plurality of arcuate grooves interposed by ungrooved portions of the roll surface distributed axially and circumferentially over the roll surface.

5. A process as in claim 1 including contacting the yarn with a snubbing means in the drawing zone.

6. A process as in claim 5 wherein the yarn contacts a heating means after passing over the snubbing means and before being withdrawn from the drawing zone.

7. A process as in claim 1 wherein the yarn is heated in the drawing zone.

References Cited UNITED STATES PATENTS 4,898,085 2/ 1933 Dreyfus et al 264-167 2,038,722 4/ 1936 Dreyfus et al 264-167 2,278,879 4/1942 Hunter 57-140 T 2,278,888 4/1942 Lewis 264-167 3,483,593 12/1969 Marlborough et al. 264-290 R 3,487,619 1/1970 Field 264-210 F 3,491,418 1/ 1970 Nicita 264-290 R JAY H. WOO, Primary Examiner US. Cl. X.R. 

